Ganita Manjari Class 9 Maths Chapter 12 Quadrilaterals Solutions

Chapter 12 Quadrilaterals: key results and formulas

• A quadrilateral is convex when all its internal angles are less than 180°, or equivalently when its diagonals intersect.
• A quadrilateral is a parallelogram if opposite sides are equal, or opposite angles are equal, or the diagonals bisect each other, or one pair of opposite sides is equal and parallel.
• Midpoint Theorem: the segment joining the midpoints of two sides of a triangle is parallel to the third side and half as long.
• The medians of a triangle meet at the centroid, which divides each median in the ratio 2 : 1.
• The midpoints of the sides of any quadrilateral form a parallelogram (Varignon). The plane can be tiled with any 4-gon.